week 7 Flashcards
what is the ancestor of all eukarya
LECA - was a single celled organism and predominantly reproduced by mitosis not meiosis
what is clonal reproduction
asexual - done by mitotic cell division by budding
what is the most to least common types of reprodcution in eukaryotes
most high eukaryotes use sexual reproduction
most higher eukaryotes that reproduce asexually can also reproduce sexually thus obligate asexual reproduction is very uncommon
do ay other domains use sexual reproduction
no, only eukaryotes have meiotic sex, other kingdoms evolved from asexual ancestors and remain asexual
define fission, budding and fragmentation
fission - division into 2 equally sized offspring
budding - unequal division, smaller offspring
fragmentation - parent breaks into many new individuals
define parthanogenesis
reproduction from an ovum without fertilisation, evolved recently and produces clones, is a type of apomixis
develops organisms from the egg cells
define apomixis
asexual reproduction without fertilisation in plants, leads to genetic clones of the parent plant
describe the main benefits and costs of sexual reproduction
benefits: promotes genetic variation within a genome of a species, more likely to survive diseases and adapt to new environments
costs: need 2 individuals to reproduce, costly for R number, locating a male of the correct species and sex is complex
describe the main benefits and costs of asexual reproduction
benefits: simple, time and energy efficient as you dont need to find a mate, can exploit suitable environments quickly
costs: limited genetic variation in species, vulnerable to changes in conditions and disease more likely to affect whole population
explain the roles of asexual and sexual reproduction in Daphnia in relation to environmental conditions
uses a mixed strategy of sexual and asexual at different times during the year to take advantage of good environmental conditions and to use sexual reproduction to enable darwinian selection when environmental conditions change
is evolving from a sexual and an asexual reproducer beneficial
no, it is an evolutionary dead end and ultimately leads to extinction due to accumulation of harmful mutations and lack of genetic diversity
discuss species that use only asexual means of reproduction may have evolved relatively recently from sexual species
species like the amazon molly and whiptail lizard have been found to have evolved from hybridisation between 2 sexually reproducing species, there is an absence of old asexual lineages further showing how it is an evolutionary dead end
explain a brief history of banana cultivation
All commercial bananas are one cultivar – Cavendish.
* Cavendish plants are sterile (no seeds) –
asexual reproduction.
* All plants are clones.
* They are ALL susceptible to Panama disease Race 4 which is wiping out the Cavendish plants in many locations.
what is Panama disease and what is it caused by
fungal disease affecting cavendish bananas, most devasting strain Tropical Race 4(TR4)
what is the red queen hypothesis
species must continuously evolve just to survive as their predators and pathogens are also evolving eg host-parasite arms race
why do pathogens evolve more quickly than their hosts
shorter generation times, faster mutation rates, larger populations and horizontal gene transfer
name some human pathogens that have evolved within living memory
HIV, COVID, drug resistant bacteria
how was the SRY gene discovered that is controls mammalian sex determination
individuals with an XY karyotype but missing part of the Y chromosome developed as females, suggesting a crucial gene on the Y chromosome controlled male development.
Studies of XX males (who had a small part of the Y chromosome translocated to an X chromosome) further suggested a single gene was responsible for initiating male development.
Cloning and sequencing of the Y chromosome led to the discovery of SRY, which encodes a transcription factor essential for testis development.
what are the functions of transcription factors
proteins that regulate gene expression by binding to specific DNA sequences. SRY protein encodes male gonadal differentiation
define an “indifferent gonad”
in early development the gonads are “indifferent” meaning they could become either an ovary or a testis
they develop from the genital ridge and remain undifferentiated until sex determination signals act
what is the major anatomical difference in males
SRY activates SOX9, leading to testis formation.
Testes produce Anti-Müllerian Hormone (AMH), which degenerates the Müllerian ducts (which would otherwise form female structures).
Leydig cells produce testosterone, stimulating development of male reproductive structures.
what is the major anatomical difference for females
No SRY = No SOX9 activation → Gonads develop into ovaries.
Müllerian ducts persist and develop into fallopian tubes, uterus, and upper vagina.
Wolffian ducts degenerate due to the absence of testosterone.
what does the presence and absence of the SRY gene result in
present: SOX9 = testis transformation
Sertoli cells secrete Anti-Müllerian Hormone (AMH) → Müllerian ducts degenerate
Leydig cells produce testosterone → Stimulates Wolffian duct to form epididymis, vas deferens, and seminal vesicles
DHT (Dihydrotestosterone) causes external male genital development
Absence of SRY (Female development):
No AMH, so Müllerian ducts develop into female reproductive structures
No testosterone, so Wolffian ducts regress
Ovaries develop and later produce oestrogen, promoting female differentiation
what are the anatomical changes in males from indifferent genitals into male gametes
genital tubercle = penis
urogenital folds = penile urethra
labioscrotal swellings = scrotum
what are the anatomical changes in females from indifferent genitals into female gametes
Without DHT Influence:
Genital tubercle → Clitoris
Urogenital folds → Labia minora
Labioscrotal swellings → Labia majora
name the structures in the indifferent stage of genital development
gonad, mullerian duct, wolffian duct, genital tubercle, urogenital folds, labioscrotal swellings
define polyspermy
the entry of multiple sperm into the egg which leads to an abnormal number of chromosomes and embryo death
define toti and pluripotent
totipotent - cells that have the potential to make all types of cell in an organism
pleuripotent - restricted potential but still able to make more than one cell type
explain the main steps in fertilisation
it creates a single diploid cell called a zygote, which divides and ultimately gives rise to all of the cells of the adult multicellular organism and thus is totipotent
describe the early animal development stages
- zygote formation where the fertilized egg undergoes cleavage (rapid mitotic divisions)
- cleavage and morula formation - cells divide without growth formimg a solid ball of cells
- blastula stage - morula becomes a hollow ball of cells (blastula in non-mammals and blastocyst in mammals). In mammals the blastocyst contains the trophoblast which forms the placenta and the inner cell mass which becomes the embryo
- gastrulation - the blastula reorganises into 3 germ layers
name the 3 germ layers (primoradial tissue type) and what they turn in to
ectoderm - skin, nervous system
mesoderm - muscle, bones, circulatory system
endoderm - digestive and respiratory systems
what is the significance of trophoblasts in mammalian embryos
the trophoblast is the outer layer of the blastocyst that does not contribute to the embryo itself but instead forms the placenta.
it supports implantation, provides nutrients and supresses the maternal immune response
describe the structure of the placenta and its main function in development
made up of blood vessels and chorionic villi that increase the surface area for exchange
provide nutrients and gas exchange to the foetal blood, removes waste eg CO2, hormone production and immune protection
define cell lineage
used to describe both the pattern of cell divisions by which a particular cell or group of cells are born, and the processes of differentiation that make it different from other cell types
define differentiation
cells specialising into different types eg mucle nerve skin
define cell fate determination
early embryonic cells become committed to specific roles
define morphogenesis
the organisation of cells into tissues, organs and body structures using cell movements, growth and apoptosis
define inductive signalling
cells influence their neighbours through chemical signals
define monoblastic, diploblastic and triploblastic
monoblastic- sponges, one layer of blast cells
diploblastic - radial symmetry - organised structure eg jellyfish, the have a back and a front, in ventral side single orifice combined mouth and anus
- 2 layers of blast cells, digestive cavity with one opening
- triploblastic - bilateral eg fish
- flies and humans, three layers of embryonic blast cells, each layer restricted to different future potentials - mouth anus and gut inbetween
define gastrulation
movement and reorganisation of cells that is linked to creation of three fundamental layers of blast or stem cells in early embryo. termed ectoderm, mesoderm and endoderm
how have model organisms such as the fruit fly Drosophila melanogaster have played a critical role in our current understanding of the molecular principles of development.
Short life cycle (rapid reproduction).
Easily observable mutations (e.g., homeotic transformations).
Highly conserved genetic pathways shared with humans.
define homeotic genes
master regulators of body plan development, specifying segemtn identity
mutations in HOX genes can cause body parts to form in incorrect location
describe at least two phenotypes associated with mutation in the key regulators of development.
- antennapedia mutation
- mutation in the Antp gene leads to legs growing where antenna should be - ultrabithorax mutation
- mutation in the Ubx gene results in a second pair of wings growing on flies
how is gene expression externally regulated
- chemical gradients
- cell-cell communication
- mechanical forces
